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Re: Apparent weight



Leigh said:

You will find that conservation of momentum is a principle that works
quite well in the horizontal plane in an accelerated frame. There is no
need to give it up. I'm very curious about how you teach your students
the first law of motion. I start by showing my students that we don't
live in an inertial frame. The first law is not trivial by any means;
it is a great intellectual feat to abstract to an environment one has
never experienced for any appreciable time - and lived to tell of it!

Howdy,

The First Law is an interesting case. I treat its statement first as
placing a body in a place where there are NO forces acting upon it (very
difficult to find that place though) and second (and most important) the
separation of objects at rest from other constant velocities in its
original form as a direct statement that Aristotle (the only "natural"
state of motion is rest) is wrong. The First Law indirectly defines an
inertial reference frame too: it is only true in inertial frames.

In some sense the First Law is contained in the Second Law except that I
believe that trivializes it a bit.


Hmm... I've got some rare earth magnets I should show you.

Magnets don't radiate angular momentum (presumably in the form of
photons). Classically they should, of course, because they produce
their fields by circulating net currents, necessitating the
acceleration of charges. Bohr was among the first to suggest that
somehow this sort of circulation did not always imply radiation,
even though classical electrodynamics says it does.

Leigh

Is the principle force that binds the atoms and molecules together the
magnetic force in these magnets? I still wonder why it takes the Central
Force assumption to derive the macroscopic rotational motion relation.
Can someone derive it from the particle equations without that assumption?

Good Luck,

Herb Schulz
(herbs@interaccess.com)